This invention relates to centrifugal pumps, and, more particularly, to an improved impeller hub assembly for centrifugal pumps.
Centrifugal pumps are well known and widely used in many different environments and applications. A centrifugal pump typically includes a wheel fitted with vanes or blades, known as an impeller. The impeller imparts motion to the fluid which is directed through the pump. A centrifugal pump provides a relatively steady fluid flow. The pressure for achieving the required head is produced by centrifugal acceleration of the fluid in the rotating impeller. The fluid flows axially toward the impeller, is deflected by the blades, and flows out through apertures between the blades. Thus, the fluid undergoes a change in direction and is accelerated. This produces an increase in the pressure at the pump outlet. As the fluid leaves the impeller, the fluid may first pass through a ring of fixed diffusion vanes surrounding the impeller, commonly referred to as a diffuser. In this device, with gradually widening passages, the velocity of the liquid is reduced, and its kinetic energy is converted into pressure energy. In some centrifugal pumps, however, there is no diffuser and the fluid passes directly from the impeller to the volute. The volute is a gradual widening of the spiral casing of the pump.
Centrifugal pump impellers typically include an integrally formed impeller hub. The impeller hub, which may be cylindrical in configuration, extends axially upstream of impeller blades and rotates with the impeller. Alternatively, the impeller hub is truncated so that it does not extend axially from the inlet side of the impeller. All pump impellers, including those with integrally formed hubs or those with little or no hub, experience flow re-circulation at reduced flow rates, and typical solids handling impeller designs experience flow re-circulation over most of the usable flow range of the pump.
Impellers are used to pump liquefied materials that may contain fibrous strands of matter. The fibrous strands of matter may comprise, for example, recycled waste paper stock, plastic fibers from newspaper banding, plastic book covers, and soft drink containers, along with metal staples or other foreign matter that may be contained therein.
When liquefied materials containing fibrous material are pumped through impellers with integrally formed hubs, there is a tendency for the long fibers to wrap around the impeller hub, to collect in dead spaces where there is no through flow, to accumulate, and block the flow of liquid to and through the impeller. This type of pump blockage is especially problematic for, although not limited to, pumps having cylindrical shaped impeller hubs that extend upstream or in front of the impeller vanes.
Pumps having little or no extending hub at the inlet are also prone to blockage. For example, when pumping liquid that includes long stringy fibers with impellers having little or no hub at the inlet, the fibers that are lighter (lower in density) than the pumped liquid will collect in the eye of the impeller when there is suction flow re-circulation in the impeller. The rotation of the re-circulating liquid forces the fibers to the center of the impeller eye by centrifugal force, thus forming a ball which blocks the inlet flow to the impeller.
An improved impeller apparatus for centrifugal pumps and method for avoiding the aforementioned problems are therefore desirable.
Briefly described, the invention provides an impeller assembly for centrifugal pumps. The assembly includes an impeller having an axially outwardly extending hub with a loose conical sleeve rotatably mounted thereon. The assembly reduces blockage encountered on the inlet side of the impeller when pumping liquefied materials.
In one embodiment, the impeller assembly includes an impeller having an inlet side and a bearing hub, wherein the bearing hub extends axially outward from the inlet side of the impeller. A conical sleeve is rotatably mounted on the bearing hub. The mating surfaces of either the bearing or the conical floating sleeve may be coated with a polymer to reduce surface friction. The bearing hub may also be bored to receive a drive shaft.
According to another embodiment of the invention, a method for reducing blockage at the inlet of an impeller assembly is provided and includes the step of: pumping pumpage through an impeller assembly having a conical sleeve rotatably mounted on the inlet side of the impeller.